Pyrometer

ABSTRACT

The invention provides an apparatus for measuring the temperature of a molten bath comprising a) a refractory mounting sleeve ( 1,1 ′) having an outer surface ( 2 ) for contacting the molten bath and an inner cavity ( 3 ), said inner cavity having an inner surface ( 4 ), an outer opening ( 6 ) and an inner closed end ( 5 ); and b) an optical pyrometer ( 7 ) attached to the mounting sleeve and adapted to measure the thermal radiation emitted by a measurement zone ( 10 ) located inside the inner cavity of the mounting sleeve and under the molten bath level. The inner cavity outer opening ( 6 ) is adapted to receive fixedly the optical pyrometer ( 7 ). The apparatus is characterized in that the mounting plate ( 8 ) is adapted to engage in a complementary recess located at the inner cavity outer opening ( 6 ) of the mounting sleeve ( 1,1 ′). Thereby, the accuracy and reproducibility of the measure is greatly increased.

FIELD OF THE INVENTION

The present invention relates to an apparatus for measuring thetemperature of a molten bath, to a refractory mounting sleeve for use insuch an apparatus and to a particular assembly of an optical pyrometerwith a refractory tube.

BACKGROUND OF THE INVENTION

A molten bath, for example a molten metal bath can have a temperature ofup to 1800° C. or higher, and often needs to be monitored closely andaccurately in order for many reactions or operations in the molten bathto be properly controlled. Normally, such an environment is destructivefor thermocouples or other monitoring type-devices.

Radiation pyrometry, more commonly called optical pyrometry, measuresthe temperature of a substance by measuring the thermal radiationemitted by the substance. Thermal radiation is a universal property ofmatter that is present at any temperature above absolute zero. Foroptical pyrometry, the useful part of the thermal radiation emitted bymost substances is continuous over a spectral range of approximately 0.3to 20 μm. This spectral range encompasses the ultraviolet (UV)radiation, up to 0.38 μm; the visible (VIS) range, from 0.38 to 0.78 μm;and the infrared (IR) radiation, from 0.78 to 20 μm. IR radiation isfurther divided into three segments, near IR (0.78 to 3 μm), middle IR(3 to 6 μm) and far IR (above 6 μm). The distribution of the thermalradiation of a substance over the spectral range is a function of boththe temperature and emissivity of the substance. Higher temperaturesshift the distribution toward the shorter wavelengths. Higher emissivityincreases the thermal radiation at a given temperature, whereas loweremissivity reduces the thermal radiation at the same temperature.Optical pyrometry utilises the radiating and propagating properties ofmatter to ascertain the temperature of a substance by measuring theintensity of the thermally radiated UV, VIS or IR energy of thesubstance.

In a known method, an optical monitoring device (optical pyrometer) isplaced above the molten bath to measure the bath temperature. However,the temperature can be difficult to measure because an insulating slaglayer is generally present over the molten bath and acts as a shield forthe optical monitoring device. Further, dust can be generated in thespace above the slag layer and can partially block the optical measuringdevice, thereby providing an inaccurate measurement of the temperatureof the bath.

U.S. Pat. No. 5,302,027 discloses an apparatus for measuring thetemperature of a molten bath which eliminates part of the problemsdiscussed above. This apparatus comprises: a) a refractory mountingsleeve having an outer surface for contacting the molten bath and aninner cavity, said inner cavity having an inner surface, an outeropening and an inner closed end; and b) an optical pyrometer located onthe top of the mounting sleeve and adapted to measure the thermalradiation emitted by a measurement zone located inside the inner cavityof the mounting sleeve and under the molten bath level. This apparatusis partially immersed in a molten bath. The principle of the measurementmethod using this apparatus is based on the fact that the thermalradiation emitted by the refractory material used as mounting sleeve islinked to the temperature of the molten bath. The refractory mountingsleeve acts as a shield that thermally protects the optical pyrometer,but also allows the measures to be made in a measurement zone locatedunder the insulating slag layer, deep into the molten bath level.

Applicant has observed that the temperatures measured with such anapparatus were less than accurate. Therefore, a need still exists for anew apparatus for accurately and closely measuring the temperature of amolten bath.

Applicant has also established that in use, the apparatus is subject tosuch vibrations and shocks that the zone where the measure is read (i.e.the target or measurement zone) by the optical pyrometer moves insidethe inner cavity so that accurate and reliable measures cannot beperformed. Having recognised the problem, applicant has designed a newrefractory sleeve adapted to receive fixedly the optical pyrometer sothat this problem is overcome.

SUMMARY OF THE INVENTION

According to the invention, this objective is reached with an apparatusfor measuring the temperature of a molten bath comprising

-   -   a) a refractory mounting sleeve having an outer surface for        contacting the molten bath and an inner cavity, said inner        cavity having an inner surface, an outer opening and an inner        closed end; and    -   b) an optical pyrometer attached to the mounting sleeve and        adapted to measure the thermal radiation emitted by a        measurement zone located inside the inner cavity of the mounting        sleeve and under the molten bath level, characterised in that        the inner cavity outer opening is adapted to receive fixedly the        optical pyrometer.

The mounting sleeve and the optical pyrometer must have co-operatingmeans to prevent relative movement of the pyrometer during its use sothat the measurement zone is substantially always located in the samezone in the inner cavity and, consequently, the measure is morereliable.

Therefore, according to the invention, the co-operating means preventingthe relative movement of the pyrometer during its use comprise amounting plate of the optical pyrometer adapted to engage in acomplementary recess located at the inner cavity outer opening of themounting sleeve.

The invention also relates to a refractory mounting sleeve for use in anapparatus for measuring the temperature of a molten bath, having anouter surface for contacting the molten bath and an inner cavity, saidinner cavity having an inner surface, an outer opening and an innerclosed end located under the molten bath level, the inner cavity outeropening being adapted to receive fixedly an optical pyrometer. Accordingto the invention, the refractory mounting sleeve comprises a recesslocated at the outer opening of the inner cavity adapted to receivefixedly the optical pyrometer so that all relative movements thereof areeliminated. Consequently, the refractory mounting sleeve solves theabove problem which was due to vibrations and shocks causing themeasurement zone of the optical pyrometer to move inside the innercavity so that accurate and reliable measures could not be performed.

According to a particularly preferred variant of the invention, therecess is frustoconical.

According to another embodiment of the invention, the inner cavity isstraight so that, should the measurement zone move, the risk of havingthe said measurement zone located, for example on a shoulder in theinner cavity is eliminated. It is of course to be understood that thisstraightness feature does not apply to the inner cavity outer openingzone which, as indicated above, can be recessed.

Advantageously, the inner closed end of the inner cavity issubstantially comprised in a plane perpendicular to a longitudinal axisof the mounting sleeve. In such a case, the inner closed end can providea measurement zone which is substantially homogeneous, and,consequently, the temperature measurement is extremely accurate andreliable.

According to a variant of the last embodiment, the inner closed end issubstantially spherical. The curvature of the inner closed end ispreferably calculated so that the distance between the measurement zoneand the optical pyrometer remains substantially constant, even in caseof minute displacement of the optical pyrometer.

The applicant has also observed that another source of inaccuracy in themeasurement can be due to the emission of fumes or other volatilecompounds by the refractory material when brought to the temperature ofuse. These fumes or other volatile compounds can condense on the opticalpyrometer (generally on the sighting tube), blocking thereby, fully orpartially the measuring ability. In certain cases, the emission of fumeor other volatile compounds also led to serious damages of the opticalpyrometer. Therefore, according to a preferred embodiment, therefractory mounting sleeve is designed to avoid or limit the emission offumes or other volatile compounds.

Conventional refractory materials used for the manufacture of protectivesleeves for temperature-measuring devices are generally copressed andcomprised of 45 to 70 weight % of alumina and 55 to 30 weight % ofcarbon. The shaped material is then fired at a temperature comprisedbetween 800 and 1100° C. This material shows excellent thermal-shock,chemical and corrosion-resistance.

Although commonly used for conventional pyrometry, in use, this materialproduces important fumes or other volatile compounds emission and cannotbe reliably used in optical pyrometry.

According to a particular aspect of the invention, the materialconstituting the mounting sleeve is fired at a temperature above 1200°C. and preferably around the temperature of use of the material,reducing thereby dramatically the fumes or other volatile compoundsemission while keeping the excellent resistance of the material.

According to a preferred variant, the refractory mounting sleevecomprises a refractory tube incorporated into the inner cavity. Therefractory tube is preferably at least partly comprised of a materialwhich completely eliminates the fume or other volatile compoundsemission problems. Preferably, the material is gas-tight so that theingress of volatile compounds or others fumes through the walls of thetubes are avoided. Suitable materials comprise alumina based materialssuch as corundum or mullite (for example the ZYALOX™ tubes from thecompany VESUVIUS Mc DANNEL), zirconia (for example the ZYAZIRC™ tubesfrom the company VESUVIUS Mc DANNEL), pure graphite, silica, molybdenumand the like. Preferably, the tube walls are thin enough, for examplebetween 0.5 and 5 mm, to avoid increasing the response-time of thetemperature-measurement. It is also advantageous that the tube fitsclosely the inner cavity of the mounting sleeve to avoid the formationof an insulating layer between the outer surface of the tube and theinner surface of the mounting sleeve. In a variant, a heat-conductingcement can be used to secure the tube in the inner cavity.

The refractory tube can be inserted or copressed with the mountingsleeve. The insertion of the tube is preferred as it permits re-usingthe tube.

According to yet another of its aspect, the invention relates to anassembly of a tube and an optical pyrometer, the optical pyrometer beingset to measure the thermal radiation emitted by a measurement zonelocated inside the tube and the tube being adapted to be inserted intoan inner cavity of a refractory mounting sleeve. Such an assembly isextremely advantageous since, beside the problem of low reliability dueto the problem of gas or fumes emission, the assembly, which can bepre-mounted and only needs to be inserted into the refractory mountingsleeve, reduces tremendously the on-site necessary hand-work. Further,the assembly can be easily reused when the refractory mounting sleeve isworn.

Preferably, the assembly comprises means allowing the control of theatmosphere inside the tube. For example, the tube or the opticalpyrometer may have a gas exhaust outlet allowing to remove, reduce orreplace the atmosphere comprised inside the tube.

Advantageously, at least in the measurement zone, a material with a highemissivity at the temperature of use is present (such as very puregraphite) increasing thereby the accuracy of the temperaturemeasurement. This material can be present as a pastille at the innerclosed end of the inner cavity or of the tube.

To facilitate a better understanding of the invention, it will now bedescribed with reference to the figures illustrating particularembodiments of the invention, without however limiting the invention inany way.

BRIEF DESCRIPTION OF THE DRAWINGS

In these figures,

FIG. 1 shows a schematic view of an apparatus for measuring thetemperature of a molten bath comprising a mounting refractory sleeveaccording to a first embodiment of the invention;

FIG. 2 shows a schematic view of an apparatus for measuring thetemperature of a molten bath comprising a mounting refractory sleeveaccording to a second embodiment of the invention;

FIG. 3 shows a schematic view of a tube which can be inserted in themounting sleeve such as the one depicted at FIG. 2;

FIG. 4 shows a schematic view of a mounting sleeve with a tube insertedtherein

FIG. 5 shows an assembly of an optical pyrometer and a tube.

DETAILED DESCRIPTION OF THE INVENTION

Visible on FIGS. 1, 2 and 4 are the refractory mounting sleeves 1,1′having an outer surface 2 adapted to contact a molten bath, for examplea molten metal bath and an inner cavity 3. The inner cavity 3 has aninner surface 4, a closed inner end 5 and an outer opening 6. The outeropening 6 is adapted to receive fixedly an optical pyrometer 7. Theoptical pyrometer is schematically depicted at FIGS. 1 and 2. Itcomprises a mounting plate 8 designed to engage into a correspondingrecess present at the outer opening 6 of the inner cavity 3 and asighting tube 9 engaged into the inner cavity 3. The pyrometer 7 can beconnected to a processor through wires or cables (not shown).

In the embodiment shown on FIGS. 1 and 2, the measurement zone 10substantially coincides with the inner closed end 5 of the mountingsleeve. The straightness of the inner cavity 3 prevents inaccuracy ofthe measure which could be due to misalignment of the sighting tube 9.

In the embodiment depicted at FIG. 4, a tube 11 made from an aluminabased material is inserted into the refractory mounting sleeve 1′. Thematerial constituting the tube does not contain volatile materials, sothat the emission of fumes is prevented and the time-life of thesighting tube is largely extended.

The tube 11 depicted at FIG. 3 can also be inserted into a mountingsleeve. It comprises in the measurement zone 10, a pastille 12 of amaterial selected for its excellent emissivity properties, for exampleultra-pure graphite.

FIG. 5 shows an assembly of an optical pyrometer 7′ and a tube 11. Theassembly can be easily and quickly inserted into a refractory mountingsleeve 1′ (not visible on FIG. 5) so that on-site handwork is reduced.In the embodiment shown, the sighting tube 9 of the optical pyrometer isengaged into the tube 11. A gas-tight connection can be obtained withconventional sealant (not shown). The optical pyrometer 7′ is set tomeasure the temperature in the measurement zone 10. Advantageously, theoptical pyrometer 7′ comprises a mounting plate 8′ adapted to engageinto a corresponding recess located at the outer opening 6 of therefractory mounting sleeve 1′.

REFERENCES

-   1. Refractory mounting sleeve-   2. Outer surface-   3. Inner cavity-   4. Inner surface-   5. Inner closed end-   6. Outer opening-   7. Pyrometer-   8. Mounting plate-   9. Sighting tube-   10. Measurement zone-   11. Tube-   12. Pastille

1. Apparatus for measuring the temperature of a molten bath, the moltenbath having a top surface, the apparatus comprising: a) a refractorymounting sleeve having an inner surface defining an inner cavity and ameasurement zone located under the top surface of the molten bath, andan outer surface including a closed end and defining an opening locatedabove the top surface of the molten bath, the opening including arecess; and b) an optical pyrometer comprising a mounting plate thatcomplementarily and fixedly engages the recess of the opening, so as toalign the pyrometer with the mounting sleeve, the pyrometer capable ofmeasuring thermal radiation emitted by the measurement zone. 2.Apparatus of claim 1, wherein the recess is frustoconical.
 3. Apparatusof claim 1, wherein the inner cavity is substantially straight. 4.Apparatus of claim 1, wherein the refractory sleeve comprises a materialwith reduced emission of volatile compounds at use temperatures. 5.Apparatus of claim 1, wherein the inner surface comprises a refractorytube.
 6. Apparatus of claim 5, wherein the tube has a wall thicknessfrom 0.5 to 5 mm.
 7. Apparatus of claim 5, wherein the tube comprises amaterial with reduced emission of volatile compounds at usetemperatures.
 8. Apparatus of claim 5, wherein the tube includesalumina.
 9. Apparatus of claim 1, wherein at least a part of themeasurement zone has an emissivity higher than or equal to theemissivity of carbon.
 10. Apparatus for measuring the temperature of amolten bath, the molten bath having a top surface, the apparatuscomprising: a) a refractory tube including an inner surface with ameasurement zone located under the top surface of the molten bath, andan outer surface including a closed end and defining an opening locatedabove the top surface of the molten bath, the opening including arecess; b) refractory mounting sleeve substantially surrounding theouter surface of the tube; and c) an optical pyrometer comprising amounting plate that complementarily and fixedly engages the recess ofthe opening, so as to align the pyrometer with the mounting sleeve, thepyrometer capable of measuring thermal radiation emitted by themeasurement zone.
 11. Apparatus for measuring the temperature of amolten bath, the molten bath having a top surface, the apparatuscomprising: a) a refractory mounting sleeve having an inner surfacedefining an inner cavity and a measurement zone located under the topsurface of the molten bath, and an outer surface including a closed endand defining an opening located above the top surface of the moltenbath, the opening including an unthreaded recess; and b) an opticalpyrometer comprising a mounting plate that complementarily and fixedlyengages the recess of the opening, so as to align the pyrometer with themounting sleeve, the pyrometer capable of measuring thermal radiationemitted by the measurement zone.